Generally, when a fixed object is fixed to a molded good made from thermoplastic resin, at first a welding boss monolithically formed on the molded good is inserted into a fixing hole formed on the fixed object. A tip section of the welding boss projecting from this fixing hole is then heated and fused to form an expanded section larger than the fixing hole, and the fixed object is fixed to the molded goods with this expanded section.
As an example of the fixing method described above, welding equipment for plastics and a welding method using the same are disclosed in Japanese Patent No. 1735109. This known welding equipment comprises a heating element generating heat with the electric resistance, a pair of electric cables, a pipe for blowing cooling air into the inside of the heating element, and a slit for exhausting the cooling air from the pipe formed on the heating element.
In the welding method using the welding equipment for plastics, a heating element is pressed to a tip section of a welding boss projecting out from a fixed hole, a voltage is loaded to the heating element to generate heat due to the electric resistance from the heating element so that the welding boss is heated and fused. At the same time, the welding boss is pressed for forming an expanded section thereon. Cooling air is then blown to the inside of the heating element, in the state where the welding equipment for plastics is pressed with the application of the voltage stopped. The expanded section of the fused resin is rapidly cooled and solidified to complete the thermo-welding work.
With the thermo-welding method described above, as the fixed object is cooled in the state where the fixed object is being pressed to a molding good to which the object is to be fixed, the expanded section is cooled without losing the close contact between the fixed object and the molding good. With this no clearance is generated in the welded portion and a fixed item with a stable quality and without bumpy movement due to welding can be obtained.
In the thermo-welding method described above, however, as a heating element is pressed to a tip section of the welding boss projecting out from a fixing hole and cooling air is blown to the heating element in the state for cooling, the heat capacity is required to become larger in association with an increase in the volume of the welding boss. Therefore, a long period of time is required, even when the cooling air is blown thereto, until the temperature drops to the room temperature. Although heating can be performed within a short period of time because Joule heat generated by applying a voltage to the heating element is used for heating, it is not easy to shorten the period required for cooling, and the time required for cooling occupies about 70% of all the time required for welding, which makes it difficult to shorten the time required for a thermo-welding work.